Cryptology ePrint Archive: BibTeX Citation of Report 2015/268

@misc{cryptoeprint:2015:268,
    author = {Itai Dinur and Orr Dunkelman and Masha Gutman and Adi Shamir},
    title = {Improved Top-Down Techniques in Differential Cryptanalysis},
    howpublished = {Cryptology ePrint Archive, Report 2015/268},
    year = {2015},
    note = {\url{http://eprint.iacr.org/}},
}

You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.